It is certainly a possibility to completely rely on FFS for the syncing process. I think that @tambo is exploring this route. However, I still use Icedrive’s syncpairs, and use FFS to “check and correct”. So every now and then I have FFS compare my local drive with my mounted drive (which in fact represents the cloud), like this:
If FFS finds any discrepancies, I hit the synchronize button. Make sure that the settings for synchronization are set to “mirror”, so that FFS only syncs in one way, and leaves your local drive undisturbed:
Good question. I think it does, because I assume that the mounted drive reflects exactly what lives in the cloud. It doesn’t contain files itself, but is more like a portal to the cloud. (Can anyone confirm this view?) So if FFS finds no problems, the local drive and the cloud should be exactly the same. Having said that, there is still the problem of file corruption (see the comment by @Abe above), which FFS probably won’t detect.
Why wouldn’t it detect corruption? Is it because a corrupted file could still have the same date and size? And, if so, what’s the issue with a content comparison?
Yes, if the corruption means that one bit is changed (from 0 to 1, or vice versa), the file size is unaffected.
The issue with the content comparison is that FFS will try to access the files on the mounted drive, which in turn triggers the mounted drive to download them into the temp-folder and decrypt them. That is not a problem per se, but it takes a looong time and your temp-folder will explode.
However, now that I think about it, it may be worthwhile to do this anyway, once in a while (once a year or so). (tagging @Abe here)
According to the changelog, the app should now track changes made when it is not running:
“Sync: Background monitor implemented to track changes in files and folders when the app is not running, and sync when app is reopened. Windows and macOS supported.”
I upgraded to version 3.31 and did some tests. However, it still doesn’t work for me. I have waited for at least 12 hours, but the app doesn’t seem to scan my folders for changes. Are others having more success?
I thought we were also waiting on a return of the scheduled sync functionality. It seems they’ve doubled-down on detecting running changes.
Maybe it’s me, but I think there’s something messy about having two apps running to provide one service. Version 2.x was a single app that did everything and did it well.
If this new background service were to crash, would we have visibility? Or, at least, visibility at a time when it mattered? At least if the main app crashes, we know about it - and a scheduled sync is guaranteed to pick up any missed changes.
It’s already been discussed there was recognised demand for a scheduled sync, but we’ve had silence since.
(tagging 
I have waited for at least 12 hours, but the app doesn’t seem to scan my folders for changes. Are others having more success?